Hitherto, many efforts have been made to suppress fogging of a silver halide photographic emulsion and to increase photographic sensitivity. At the same time, shortening of the development processing including development, bleaching and fixing gives a great merit in practice and is another target in improving performance of a silver salt photograph. Also, a great merit can be practically provided by minimizing the change in photographic properties due to scattering of processing conditions. A highly sensitive photographic material conventionally uses in practice a silver iodobromide emulsion subjected to gold/sulfur sensitization. However, it is known that the use of silver iodobromide emulsion leads to failure in shortening of the development time due to a conspicuous development inhibitory action by the iodide ion and bromide ion released at the development and is associated with an increase of scattering in photographic properties because the ions accumulate in the processing. The ions are also known to inhibit bleaching. At the same time, the silver iodobromide emulsion is low in the solubility in water and the fixing requires a long period of time. A silver chlorobromide emulsion having a high silver chloride content and substantially free of silver iodide is known as a preferred material because it shortens respective processes of, development, bleaching and fixing and minimizes change in photographic properties due to scattering of processing conditions. On the other hand, the silver chloride emulsion is known to have a defect in that the sensitivity is generally low and, accordingly, various techniques have been proposed for rendering the silver halide emulsion having a high silver chloride content highly sensitive to overcome this defect.
European Patent 0534395A1 discloses that high sensitivity can be achieved by the use of tabular grains having {100} planes as the main planes.
The {100} tabular grain having the main planes in the form of a right-angled parallelogram is described in JP-A-51-88017 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") and JP-B-64-8323 (the term "JP-B" as used herein means an "examined Japanese patent publication"). However, either of these publications relates to a rectangular parallelopiped grain having main planes in the form of a right-angled quadrilateral with all outer surfaces being {100} planes. Also, JP-A-5-313273 describes a grain in which the main planes are in the form of a right-angled quadrilateral with four angles being asymmetrically in defect. As compared with a grain of which surfaces all are {100} planes, a grain having other crystal planes in combination is preferred because the grain surfaces can be separated in function. With respect to the functional separation of the grain surface, JP-A-2-34, JP-A-1-201651 and JP-A-2-298935 may be referred to.
However, the high silver chloride emulsion usually has {100} planes and a high silver chloride emulsion of grains having planes other than the {100} plane, for example, a {111} plane, requires the use of a special technique and not so many investigation examples are present thereon. Journal of Photoqraphic Science, Vol. 21, p. 39 (1973) reports only that a silver chloride grain having a {111} plane can be produced by using dimethylurea but does not refer to photographic properties of the grain. In International Congress of Photographic Science, Rochester (1978), Wyrsh reported that a grain having a {111} plane can be prepared by using a cadmium compound and ammonia. Wyrsh reported that on comparison between a grain having a {111} plane and a grain having a {100} plane on the photographic sensitivity using a sulfur sensitized emulsion, the difference therebetween is not so great but the grain having a {100} plane shows a slightly higher ultimate sensitivity. JP-A-55-26589 discloses that a silver chloride grain having a {111} plane can be obtained by forming the grain in the presence of a merocyanine dye. However, the high silver chloride grain having a {111} plane disclosed in the above-described patent application is not intended as a highly sensitive photographic material and the disclosure is only to show that the restriction in the addition method of a dye is useful irrespective of the crystal plane or composition of the grain. Accordingly, although the high silver chloride emulsion is well known as a preferred material for shortening the processing, it has been considered difficult from a technical viewpoint to produce a high silver chloride photographic material having high sensitivity because conspicuous fogging is caused when chemical sensitization is sufficiently effected so as to achieve high sensitivity. Also, it is a matter of ordinary knowledge that gold sensitization is accompanied by the increase in fogging and thus, it is the status quo that no satisfactory technique has been reached for subjecting a high silver chloride emulsion to sufficient gold/chalcogen sensitizations which are considered essential in the case of a highly sensitive photographic material.